1. Field of the Invention
The present invention relates to a device for correcting torque detected by an electric dynamometer which is made up of a rotary machine, i.e., which is made up of a motor or a generator.
2. Description of the Prior Art
There has been proposed an electric dynamometer which is made up of a rotary machine, and specifically a dynamometer (hereinafter referred to as operation-type dynamometer) of the type which does not employ a swinging mechanism for the stator or a weighing device to measure the torque, but which detects the armature current, armature voltage, rotation speed or field magnetic flux thereby to calculate the torque relying upon the detected values. In this operation-type dynamometer, the torque T.sub.M which acts between the yoke and the armature of the dynamometer is corrected by taking into consideration the friction torque T.sub.X of the bearings, windage-loss torque T.sub.Y of the rotor and eddy-current-loss torque T.sub.Z in the armature, thereby to precisely find the torque. Namely, the torque T calculated by the operation-type dynamometer is given by the following equation, EQU T=T.sub.M -(T.sub.X +T.sub.Y +T.sub.Z + . . . ) (1)
FIG. 1 is a graph illustrating a relation between the rotation speed N and the above-mentioned loss torques T.sub.X, T.sub.Y and T.sub.Z, in which the abscissa represents the rotation speed N and the ordinate represents loss torques. The total loss torque T.sub.T represents the sum of friction torque T.sub.X of the bearings, windage-loss torque T.sub.Y of the rotor, and eddy-current-loss torque T.sub.Z in the armature.
Most of the total loss torque T.sub.T consists of friction torque T.sub.X, windage-loss torque T.sub.Y and eddy-current-loss torque T.sub.Z. The sum of these loss torques T.sub.X, T.sub.Y and T.sub.Z rises up to about several percent of the rated torque of the operation-type dynamometer. To more precisely calculate the torque, therefore, the loss torques must be corrected more precisely. In practice, therefore, the total precision of the operation-type dynamometer is determined by the precision for detecting the terms T.sub.X, T.sub.Y and T.sub.Z in the above-mentioned equation (1).
As will be obvious from FIG. 1, furthermore, the total loss torque T.sub.T does not change simply in proportion to the rotation speed N, but changes in a complicated manner. According to the conventional art, therefore, complicated mechanisms were necessary if it was attempted to correct the loss torques more precisely, and this fact resulted in the increase in the manufacturing cost of the dynamometer. Because of this reason, the operation-type dynamometer was not used extensively.